Field of the Invention
The present invention relates to a radiation imaging apparatus and a radiation imaging system.
Description of the Related Art
Radiation imaging apparatuses having arrays of pixels in which switches such as TFTs (thin film transistors) and conversion elements such as photoelectric conversion elements are combined have been put to practical use as radiation imaging apparatuses used for medical imaging diagnosis and non-destructive examination by means of radiation such as X-rays. Each switch is arranged between a conversion element and a column signal line, and by turning on a switch, a signal is read out from the conversion element via the column signal line.
Japanese Patent Laid-Open No. 2011-255020 discloses a radiation detection apparatus having a correlated double sampling unit (CDS unit). The CDS unit includes a first sample holding circuit, a second sample holding circuit, and a differential amplifier. The first sample holding circuit holds a sample of a remnant component (noise component) of a signal charge, and the second sample holding circuit holds a sample of a signal charge (noise component+signal component). The differential amplifier amplifies the difference between the output of the first sample holding circuit and the output of the second sample holding circuit.
Parasitic capacitances are formed between a column signal line for reading out signals from conversion elements and the electrodes of the multiple conversion elements in the column in which the column signal line is arranged. The column signal line and the conversion elements are capacitively coupled due to these parasitic capacitances, and thus crosstalk can occur. For this reason, when the signals are read out via the column signal lines from the conversion elements of pixels in a row, if the potential of the electrodes of the conversion elements of pixels in another row changes due to photoelectric conversion, the potential of the column signal lines can change due to crosstalk. This can cause the SN ratio of the readout signals to decrease.
Note that correlated double sampling (CDS) is a technique for canceling KTC noise, which is based on the premise that the noise component in the first instance of sampling is the same as the noise component in the second instance of sampling. Note that with usual CDS, the first instance of sampling is performed after a reset operation for the potential of the column signal line or the conversion element, and thereafter, the second instance of sampling is performed without the reset operation being performed once again. If the reset operation is performed between the first instance of sampling and the second instance of sampling, the noise component (KTC noise) sampled in the first instance of sampling will be different from the noise component (KTC noise) sampled in the second instance of sampling. Accordingly, in this case, the noise component cannot be canceled.